Supercritical (fluid) carbon dioxide (CO.sub.2) is different from conventional liquids and gases in that it is a dense fluid which is compressible like a gas but unlike a gas is pumpable like a liquid. It is desirable to pipeline CO.sub.2 as a supercritical single phase fluid, for ultimate use, e.g., as an injection fluid in tertiary oil recovery, and to have a dry fluid carbon dioxide to prevent corrosion during the transport and utilization of supercritical carbon dioxide as an injection fluid.
Generally, CO.sub.2 produced from wells is depressurized, demoisturized in the gaseous state and repressurized at the field location for pipelining in its supercritical state. This requires (1) sizable on-site equipment for depressurization, demoisturizing, pressurizing and solvent handling and (2) high energy demands. In the case of supercritical CO.sub.2, most of the conventional desiccants used for gases don't work well because supercritical CO.sub.2 is a very good solvent, and itself undesirably dissolves many potential treating solvents. Also, moisture removal is not possible unless the solvent can form a separate non-miscible phase.
U.S. Pat. No. 4,478,612 describes a process for the desiccation of supercritical CO.sub.2 using glycerol. However, commercial glycerol is expensive and some of the glycerol is lost because of solubility of glycerol in the supercritical CO.sub.2. In the above patent, it is noted that the glycerol recycled from the regenerator is 99% pure and the same is said for the prior use of triethylene glycol. Clearly, use of such high grade desiccants can be expensive and impractical at field locations.
Surprisingly, it has been found that certain compositions of glycerine with certain dioxane derivatives are good desiccant compositions for the removal of moisture from supercritical CO.sub.2 overcoming disadvantages in the use of commercial glycerol. Moreover, the new drying agents for supercritical CO.sub.2 can be obtained in an inexpensive manner as the by-products of other processes, thus, reducing the cost of desiccant but yet providing better desiccant properties for the dehydration of supercritical CO.sub.2 than various highly pure reagents of the prior art.